1. Field of the Invention
The invention relates generally to an apparatus for shifting the position of a beam of light and, in particular, to acousto-optical translators and deflectors which change the position of a beam of light without frequency shift for use in delay lines as disclosed in applicant's copending U.S. patent application Ser. No. 274,577 and in channelized receivers as disclosed in applicant's copending U.S. patent application Ser. No. 274,611, incorporated herein by reference, both of which are filed concurrently herewith.
2. Description of the Prior Art
Beam deflection can be accomplished acousto-optically as illustrated in FIG. 1 or electro-optically as illustrated in FIG. 2. Acousto-optical deflection employs a high interaction efficiency Bragg technique where the diffraction angle varies with the RF frequency (f) as follows: EQU .DELTA..theta.=(.lambda./V.sub.a).DELTA.f
where
.DELTA..theta.=.theta.'.sub.B -.theta..sub.B =.delta. PA1 V.sub.a =velocity of propagation of acoustic waves through the Bragg cell PA1 .lambda.=wavelength of incident light
Variable RF voltage source 100 is connected to a piezoelectric transducer 101 coupled to one end of Bragg cell 103 and having an absorber 102 at the opposite end thereof. Source 100 activates transducer 101 to launch acoustic waves 104 along Bragg cell 103. Incident light 105 is deflected by angular amount .delta. and frequency shifted by the frequency of the waves. By adjusting the frequency of variable RF voltage source 100, the angle .delta. may be varied and the amount of beam deflection may be changed.
FIG. 2 illustrates an electro-optical system which uses a variable electric field to generate, in a suitable crystal, a spatial refractive index gradient that is transverse to the light path of the incident light to effect beam deflection. In particular, crystal 120 is comprised of upper portion 121 and lower portion 122. Each crystal is an electro-optical crystal material having a particular crystal lattice. An electric field is applied across the interface surface 124 between portions 121 and 122 by applying potential difference 123 to metalized surfaces 126 and 127. The electric field generated by potential difference 123 causes a spatial refractive index gradient along interface surface 124 and transverse to the light path of the incident light beam. This causes the transmitted beam to bend toward the region of higher index so that the output beam 125 is deflected.